The present invention relates to the image reproducing equipment which can display imagery on a part of a display screen, and more specifically to television receivers which can display pictures of an aspect ratio different from the aspect ratio of the display screen or which can display a small sub picture, or a visual representation of information, in a large master picture.
A high definition television system employs a wide aspect ratio of 16:9, and a high definition television receiver has a wide screen to display 16:9 images, whereas a conventional NTSC or PAL television receiver has a 4:3 screen. To attain mutual compatibility, adjustment to a different aspect ratio is required. A compatible television receiver is designed to use only a center section of the screen, to display pictures of a different aspect ratio.
As shown in FIG. 7, a display screen 20 of the 4:3 aspect ratio, for instance, is divided into a center section L1 and upper and lower marginal sections L2. Valid picture signals of the 16:9 aspect ratio are displayed in the center section L1, and added invalid blank picture-signals are displayed in the upper and lower marginal sections L2.
In the case of a wide screen 20 of the 16:9 aspect ratio, as shown in FIG. 8, valid picture signals of the 4:3 aspect ratio are displayed only in a center section L1 between left and right blank marginal sections L2.
In any case, the invalid picture signal is a signal of a fixed luminance (or brightness) at the black or white level or some other level. Therefore, there is formed a sharp difference in brightness between the center section L1 and each blank marginal section L2.
In these conventional compatible television receivers, however, the division into the center section L1 and the marginal sections L2 is fixed, and pictures are always reproduced in the same center section fixed in the screen. As a result, the screen such as the fluorescent screen of a CRT deteriorates nonuniformly, rapidly in the center section, that is, and degrades the quality of picture.
The same problem arises in the case of a television receiver capable of displaying a sub picture as shown in the left lower corner of a screen 20 in FIG. 9 or visual indication of data as shown in the right upper corner of the screen 20 of FIG. 9.